Significant bone
regrowth occurs in dental implant study

Scientists at the Yerkes Primate Research Center soon will describe
findings
that may improve the reconstruction of lower jaw bones for placement of
dental
implants in human patients and the treatment of bone deformities
associated
with various diseases such as cancer.

In a scientific paper in the International Journal of Oral and
Maxillofacial
Implants' Novem-ber/December issue, the scientists reported that a large
amount of bone -- between 544 and 733 milligrams, or about one cubic
centimeter
-- was regenerated in the lower jaw bone of rhesus monkeys.

"This is the most new bone ever produced in an attempt at bone
regeneration in
the jaw bones of a primate," said Michael E. Fritz, who heads the Yerkes
Center's dental implant study. Using rhesus monkeys as their model, Fritz
and
his colleagues attempted bone regeneration as part of their National
Institute
of Dental Research-funded study designed to determine the most effective
approach for dental implants in human patients who have lost their teeth.
W.L.
Gore and Associates provided supplemental funding for the study.

Bone regeneration is crucial to restoring tissue and ultimately dental
function through dental implants, explained Fritz, who is Charles Howard
Candler Professor of Dental Medicine at Emory and Yerkes research
scientist in
pathobiology and immunobiology.

The findings may have application beyond dental implants. "When many
types of
tumors are removed, large voids in the bone can be created," Fritz
explained.
"Because the results of the study may provide information on how to fill
these
voids, our Yerkes work may provide extensive benefits for the health of
the
human population other than purely dental." About 90 percent of the gap
in the
lower jaw bone of the three rhesus monkeys involved in the study was
filled
with new bone. "These results, although preliminary, are very exciting,"
noted
Fritz.

"Until this study, it was not known that this quantity of bone
regeneration
was possible in chronic jaw bone defects without grafts from another part
of
the skeleton or the use of biotechnology agents," said Ross Hardwick of
W.L.
Gore & Associates Inc., one of the co-authors of the scientific
paper. "The
study shows that there is significant natural biologic potential for bone
regeneration."

To foster bone growth, the scientists used a specifically designed
membrane to
cover the bone defect or gap that was created when the dental implants
that
they were studying in the animals were surgically removed. The dental
implants
were extracted so that the scientists could study how well they had
functioned
in the monkeys' mouths.

Removing the dental implant and surrounding bone tissue created a large
void
in the animals' lower jaw bone, Fritz said. The gap was allowed to remain
for
six months to simulate the medical treatment of tumors of the bone or
other
conditions such as injuries from automobile accidents that destroy bone
tissue.

"When bone is lost through such diseases as cancer or by an impact
injury,
reconstructive surgery is typically not conducted for many months because
the
physicians' first priority in treatment is other issues including, in the
case
of cancer, the healing of the wound and the prevention of recurrence of
the
tumor," said Hardwick.

After the six-month period, a reinforced membrane, designed and
manufactured
specifically for this type of treatment by W.L. Gore, was placed in the
animals' lower jaw bones. The membrane acted as a passive mechanical
barrier
that prevented undesirable tissues, such as fibrous connective tissue
from the
gums, from causing scars in the gap and created space into which bone
regeneration could occur. Scar tissue could interfere with bone healing
and
growth, Fritz explained.

The membrane, shaped to fit the gap, was held in place with stainless
steel
mini screws. The animals were given general anesthesia for the surgery,
the
placement of the membrane as well as for the periodic evaluations of the
membrane site.

"We treated the monkeys very much like we treat our human patients who
have
dental problems as far as making sure that there is no discomfort during
and
after the dental procedures," noted Fritz.

The membrane site was monitored by standard X-ray and digital
subtractive
evaluations. To provide a measure of the amount of bone loss or gain
that
occurred, X-rays were made when the membrane was placed and at
three-month
intervals. The X-rays revealed bone gain in each membrane-treated site.

Clinical and histologic evaluations also were conducted over the one
year that
the membranes were monitored. One year after the membrane was placed in
the
monkeys' mouths, tests indicated no statistically significant difference
in the
incremental growth rates of the newly created bone and the old bone in
the
lower jaw.

In future studies, Fritz and his colleagues will investigate the growth
factors and other mechanisms that promote bone regeneration. "Our
research at
Yerkes may show that by adding growth factors to the membrane, bone
regeneration will be much faster," he said. "At this point, it takes 12
months
to grow mature bone back. If this time period can be abbreviated to two
months,
the patients will benefit greatly."

The scientists also will examine the characteristics of loading dental
implants -- how the regenerated bone will respond to the stress caused by
such
normal activities as eating. "To our knowledge, no one has examined the
loading
characteristics in newly created bone," he added.